Embodiments of the present invention relate to a ball valve assembly, and more particularly, a ball valve assembly for use in underwater (such as subsea) well completions.
Ball valves are mechanical devices used to control fluid flow. They comprise a generally spherical or part-spherical rotatable valve element (“ball”) with a bore therethrough, positioned within a fluid conduit. In a first, open, configuration, the bore of the ball, is substantially in line with the conduit, such that fluid may flow therethrough. As the ball is rotated., the available fluid flow path is constricted or sheared until the ball reaches a closed configuration, in which the ball's bore is not accessible to the fluid in the conduit, and so no fluid flow is possible past the ball. To enable controlled rotation of the ball, it is typically mounted on bearings and/or provided with trunnions for supporting accommodation within a support assembly.
One major application of ball valves is within underwater hydrocarbon extraction or production facilities, and in such locations may be used to control the flow of production fluid. As prior art may be noted U.S. Pat. No. 6,152,229, WO2006/040592, U.S. Pat. No. 6,698,712, US2009/0065212, US2009/0065213, WO2008/060891 and GB 2340860 for example.
When used in this way, the ball valve is operating within a harsh environment. In particular, the fluid may contain significant amounts of debris or particulate contaminants. With prior art designs such as those set out above, it is a problem that such debris may contaminate the ball valve support/actuation assembly (known as the actuation zone), preventing effective rotation of the ball. It is common for ball valves to stall before their intended life-cycle end due to debris ingress, contamination formation, corrosion, and lubrication washout. This stalling may lead to over-stressing and deformation of the rotation mechanism, rendering the valve inoperable.
In addition, ball valve assemblies may become unbalanced, so that an opening or dosing force is not applied evenly to the ball. This lack of balance may also cause over-stressing and deformation of the rotation mechanism.
It is also important to provide a failsafe mechanism, which acts to close the valve in the event of planned or unplanned venting of valve control system pressure.
Embodiments of the present invention overcome the problems described above, and thus provide a ball valve assembly suitable for use in harsh environments, such as within a well completion system.